Some key conservatives have sharply attacked Paul over the issue. Eric Erickson, who runs the conservative site Redstate, has cast the newsletters as Paul’s “Jeremiah Wright moment,” referring to President Obama’s ex-pastor.

What’s not clear is how it will impact the race in Iowa. Paul’s core base of support, which comprises about 20 percent of the vote there, is very unlikely to defect from him, as they have stuck with the congressman even as other candidates like Herman Cain have risen and then fallen. Paul backers already know the candidate has controversial views on not only race but a number of of issues because of his strong anti-government stances.

And it’s not clear if how much Republican voters in Iowa will focus on racial issues. Texas Gov. Rick Perry plunged in the polls because of his poor performance in debates; the controversy earlier this year over a parcel of land dubbed “Ni**erhead” at a hunting camp his family owned appears to have had little effect on his candidacy.

But here’s how it could hurt Paul. In the last few weeks, after months of being stuck at 20 percent in polls, the congressman has gained anywhere from three to 10 points in surveys in Iowa. Those new backers may not be the committed libertarians who have long supported Paul and could be turned off by both the language in the newsletters and his angry reaction to questioning about it and look again at other candidates.

And Paul also faces the challenge of his changing stories on the issue. As USA Todayreported on Thursday, back in 1996, Paul defended the language in the newsletters, which he has distanced himself from more recently.

“Given the inefficiencies of what DC laughingly calls the criminal justice system, I think we can safely assume that 95 percent of the black males in that city are semi-criminal or entirely criminal,” he told a Dallas Morning News reporter back then.